This invention relates generally to electric motors and, more particularly, this invention relates to efficient AC motor designs.
Electric motors (e.g., AC electric motors, also referred to in the art as xe2x80x9csynchronous motorsxe2x80x9d) are used in a wide variety applications, such as in fans to rotate a propeller blade, and in disk drives to rotate magnetic disks. To these and other ends, electric motors have two primary portions; namely, a stationary portion (xe2x80x9cstatorxe2x80x9d) that produces a varying magnetic field, and a rotational portion (xe2x80x9crotorxe2x80x9d) that rotates in response to the variations in the magnetic field produced by the stator.
The stator in a synchronous motor typically includes a winding arrangement that converts an AC input signal (e.g., 230 volts AC) into the noted varying magnetic field. Accordingly, the windings are physically located in the stator so that they energize at strategic points in the intended rotation of the rotor. Each winding thus interacts with the rotor at a specified time in the rotor rotation cycle to generate and maintain rotor rotation. For example, a stator may include three windings that each are evenly spaced 120 degrees apart within a stator housing. Each winding thus energizes at selected times to provide one third (i.e., 120 degrees) of rotational energy (known in the art as xe2x80x9ctorquexe2x80x9d) to the rotor.
There is a continuing need in the art to increase the efficiency of synchronous motors. More particularly, among other things, more efficient synchronous motors should draw less current than those that are less efficient, while at the same time providing a comparable torque. Many current synchronous motor designs, however, are not efficient and/or have a relatively complex circuit arrangement. These noted problems thus increase one or both of motor operation and manufacturing costs.
In accordance with one aspect of the invention, a stator in a synchronous fan includes first and second main windings, and an auxiliary winding. Illustratively, the first and second main windings are wound in a bifilar arrangement. In addition, the stator has a switch to switch the stator between a plurality of configurations. One of those configurations is an induction configuration that permits the first main winding to induce a voltage in the auxiliary winding when a current (e.g., a time-varying current) is transmitted through the first main winding. Moreover, the first main winding is electrically isolated from the auxiliary winding when in the induction configuration.
In illustrative embodiments, a second voltage is induced in the second main winding when a first voltage is produced by the first main winding. The (induced) second voltage in the second main winding produces the induced voltage in the auxiliary winding. Among other values, the second voltage induced in the second main winding may be no greater than about half the first voltage in the first main winding.
The first main winding may include a first input, and the second main winding may correspondingly include a second input. The voltage is induced in the auxiliary winding when no signal is applied to the second input, and a signal is applied to the first input. The stator also may have a non-induction configuration where the first and second inputs are connected to electrically connect the auxiliary winding with the first and second main windings.
In some embodiments, the voltage is induced in the auxiliary winding by a magnetic field produced by the first main winding. A capacitance may be in series with the auxiliary winding to form an auxiliary branch, which is in parallel with the second main winding. The motor also includes a rotor that interacts with the stator to rotate. The rotor receives a sufficient amount of torque when in an at rest position when the voltage is induced to begin rotating. In exemplary embodiments, the current is an AC current that, when transmitted through the first main winding, produces a voltage in the first main winding.
In accordance with another aspect of the invention, a stator circuit for use in a stator of an AC electric motor includes first and second main windings, and an auxiliary winding. The second main winding and auxiliary winding are within a first closed loop (i.e., permitting current flow). The first main winding and second main winding are connectable in a second closed loop. The first and second main windings are configured so that when in operation and not connected in the second closed loop with the second main winding, a first voltage in the first main winding induces a second voltage in the second main winding.
In some embodiments, the first main winding is wound in a bifilar configuration with the second main winding. The circuit may further have a first input in electrical communication with the first main winding, and a second input in electrical communication with the second main winding and the auxiliary winding. The two inputs are electrically connectable to form the second dosed loop. When in operation and the two inputs are not electrically connected, the first main winding is not in the second closed loop with the second main winding.
In other embodiments, when in operation and the first winding is not in the second closed loop with the second main winding, the first voltage is applied to the first input only. In still other embodiments, when in operation and the first winding is not in the second closed loop with the second main winding, the first main winding is not electrically impacted by a third voltage applied to the second input when no voltage is applied to the first input.
The second voltage may cause an auxiliary voltage in the auxiliary winding. When in use and the first main winding is connected in the second closed loop with the second main winding, the first main winding illustratively is electrically connected in parallel to the second main winding. The auxiliary winding may be physically located about 90 degrees from the first main winding within the motor. When in operation, the stator circuit is capable of applying more torque when the first main stator is in the second closed loop with the second main winding than when the first main stator is not in the second closed loop with the second main winding.
In accordance with still another aspect of the invention, a stator circuit for use in a stator of an AC electric motor has first and second main windings, and an auxiliary winding. The auxiliary winding is in electrical communication with the second main winding. The circuit further includes an apparatus for controlling the first and second main windings to be in either one of a low state and a high state. The high state provides higher torque than the low state (when in operation). When in the low state, the first main winding is electrically isolated from the second main winding. The windings are configured so that a first voltage across the first main winding induces a second voltage in the second main winding.
The controlling means also permits the windings to be in a medium state. When in the medium state, the first main winding illustratively is electrically isolated from the second main winding, and a third voltage in the second main winding has no electrical impact on the first main winding. When in the high state, the first main winding illustratively is in parallel with the second main winding, and a fourth voltage applied to the first and second main windings produces a voltage across the auxiliary winding.